Fungal endophytes of the genus Neotyphodium (formerly Acremonium) infect a number of temperate climate Pooideae grasses. The Neotyphodium endophytes can produce alkaloids which are considered to confer degrees of pest and possibly disease protection upon the plants in which they naturally occur (Rowan and Latch, 1994; Blank and Gwinn, 1992). The Neotyphodium endophytes are vertically transmitted through the seed of the grasses and no natural horizontal transmission has been established (Leuchtmann,1997).
Many of the predominating natural endophyte infections of improved grass cultivars used for pastoral agriculture production also cause significant animal disorders, for example tall fescue toxicoses (Stuedemann and Hoveland, 1988) and ryegrass staggers (Fletcher et al., 1999). These may be complex toxic reactions by animals to alkaloids produced under a range of plant growth conditions. Significant economic loss within pastoral agriculture systems can occur due to such animal toxicoses. On the other hand presence of at least some endophytes may be essential for the competitive persistence of the chosen grass in a pasture (Elberson and West, 1996, Fletcher and Easton, 2000).
Grass lines can be artificially infected with selected endophytes. Axenic cultures of endophytes can be used to infect grass seedlings, grown initially under sterile conditions (Latch and Christensen, 1985), which are then selected for desirable qualifies, and multiplied for commercial use. Three significant examples of this technology have been developed by the Grasslands division of AgResearch Ltd: GREENSTONE™ tetraploid hybrid ryegrass with ENDOSAFE™ endophyte (Tapper and Latch, 1999, NZ Patent 233083); various perennial and hybrid ryegrasses with AR1 endophyte (Fletcher and Easton, 2000); and tall fescue cultivars with MaxQ™ endophyte (Bouton, 2000; Bouton et al., 2002, U.S. Pat. No. 6,111,170).
Fescue Toxicosis
Fescue toxicosis has been associated with the natural infection of tall fescue by common strains of Neotyphodium coenophialum. These strains typically produce the ergopeptine alkaloid, ergovaline, which is of a class of ergopeptines known to be toxic to mammals. Ergovaline is considered to be the primary cause of fescue toxicity. Other compounds, notably other ergoline and ergolene compounds, for example lysergic acid, possibly add to the syndrome (Oliver, 1997; Gadberry et al., 1997; Hill et al., 2001).
The ergovaline levels tend to be higher in leaf sheath and heads of tall fescue than in leaf blade and undergo seasonal variation (Rottinghaus et al., 1991). There is very little ergovaline in roots. Typically a concentration of ergovaline in herbage or herbage products such as hay, straw, seed or silage of greater than an average of 0.4 ppm of dry matter has been considered a risk of causing fescue toxicosis (Tor-Agbidye et al., 2001) especially when combined with climatic conditions exacerbating fescue toxicosis symptoms.
Other Compounds Recognised as Plant Defence Mechanisms—Peramine, Lolines
Peramine is produced in endophyte-infected grass (Rowan et al., 1986) and probably mobilised within the plant. It is a potent feeding deterrent for a range of insects, e.g. Argentine stem weevil (Listronotus bonariensis), (Rowan and Latch 1994) and a significant factor for protecting endophyte-infected grasses from insect pest predation.
Lolines (N-formylloline, N-acetylloline, N-acetyinorloline and other closely related compounds) are produced by some Neotyphodium endophytes including N. coenophialum typical of tall fescue. These compounds in appropriate endophyte-infected grasses have properties of deterring or resisting a number of insects, notably sucking insects, for example, Rhopalosiphum padi (Seigel et al., 1990).
Protective Effects in Tall Fescue Pastures—Persistence under Stress Conditions
Endophyte infection has been associated with enhanced persistence of tall fescue plants under water deficit or drought conditions. Whether this effect is due to better resistance of biotic stress factors expressed in water deficit situations; general better health of endophyte-infected tall fescue plants (particularly of root systems); or due to specific differential physiological responses of the endophyte-infected plants to water stress; is not clearly evident. However, the overall effect is enhanced resistance to water deficit.
Tremorgens
Some Neotyphodium endophytes, notably those of evolutionary derivation from strains of Epichloë festucae such as N. lollii, produce potent tremorgens which are toxic to grazing animals. To ensure such tremorgens are not produced by an endophyte artificially introduced into forage tall fescue or ryegrass, the presence of the known potent tremorgens typical of endophytes, that is the lolitrems, is tested for. Also tremorgenic activity in grazing test animals is looked for.
It is an object of the present invention to provide an endophyte which can produce ergovaline and some ergoline and ergolene compounds at the base of the tall fescue leaf sheaths and in the crown of the plant but only in a manner such that the usual concentration in herbage as generally consumed by grazing animals in common farming practice is less than a practical threshold toxicity level.
For the purposes of this specification “crown” is defined as that area of a grass plant which is generally less than 2 cm above soil level and excludes the roots of the grass, but includes the base of tillers and lateral meristem growing points for new vegetative tillers.
It is a further object of the invention to provide an endophyte which can produce lolines in amounts which are considered to be partially or substantially effective in deterring some insect pests from feeding on plants.
It is a further object of the invention to provide an endophyte which does not produce detectable levels of lolitrems and are not observably tremorgenic.
It is a still further object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.